Integrated fuel cell stack thermostat

ABSTRACT

A fuel cell system includes a fuel cell stack and a thermostat. The thermostat is mounted to the fuel cell stack to regulate a flow of coolant.

BACKGROUND

The invention generally relates to an integrated fuel cell stackthermostat.

A fuel cell is an electrochemical device that converts chemical energyproduced by a reaction directly into electrical energy. For example, onetype of fuel cell includes a polymer electrolyte membrane (PEM), oftencalled a proton exchange membrane, that permits only protons to passbetween an anode and a cathode of the fuel cell. At the anode, diatomichydrogen (a fuel) is reacted to produce hydrogen protons that passthrough the PEM. The electrons produced by this reaction travel throughcircuitry that is external to the fuel cell to form an electricalcurrent. At the cathode, oxygen is reduced and reacts with the hydrogenprotons to form water. The anodic and cathodic reactions are describedby the following equations:H₂→2H⁺+2e⁻ at the anode of the cell, and   Equation 1O₂+4H⁺+4e⁻→2H₂O at the cathode of the cell.   Equation 2

A typical fuel cell has a terminal voltage near one volt DC. Forpurposes of producing much larger voltages, several fuel cells may beassembled together to form an arrangement called a fuel cell stack, anarrangement in which the fuel cells are electrically coupled together inseries to form a larger DC voltage (a voltage near 100 volts DC, forexample) and to provide more power.

The fuel cell stack may include flow plates (graphite composite or metalplates, as examples) that are stacked one on top of the other, and eachplate may be associated with more than one fuel cell of the stack. Theplates may include various surface flow channels and orifices to, asexamples, route the reactants and products through the fuel cell stack.Several PEMs (each one being associated with a particular fuel cell) maybe dispersed throughout the stack between the anodes and cathodes of thedifferent fuel cells. Electrically conductive gas diffusion layers(GDLs) may be located on each side of each PEM to form the anode andcathodes of each fuel cell. In this manner, reactant gases from eachside of the PEM may leave the flow channels and diffuse through the GDLsto reach the PEM.

The fuel cell stack typically is part of a fuel cell system thatcirculates a coolant through the stack for purposes of regulating atemperature of the stack. More specifically, a coolant subsystem of thefuel cell system may include a coolant pump that establishes a coolantflow through the fuel cell stack to remove thermal energy from thestack; and the coolant subsystem may include a radiator to removethermal energy from the coolant flow after the flow exits the fuel cellstack.

SUMMARY

In an embodiment of the invention, a fuel cell system includes a fuelcell stack. The fuel cell system also includes a thermostat that ismounted to the fuel cell stack to regulate a flow of coolant.

Advantages and other features of the invention will become apparent fromthe following drawing, description and claims.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic diagram of a system to regulate a flow of coolantthrough a fuel cell stack according to an embodiment of the invention.

FIG. 2 is a top view of an end plate of a fuel cell stack according toan embodiment of the invention.

FIG. 3 is a side view of the end plate according to an embodiment of theinvention.

FIG. 4 is a bottom view of the end plate according to an embodiment ofthe invention.

FIG. 5 is a cross-sectional view taken along line 5-5 of FIG. 2according to an embodiment of the invention.

FIG. 6 is a more detailed schematic diagram of a portion of the systemof FIG. 1 depicting the integration of a stack thermostat into the fuelcell stack according to an embodiment of the invention.

FIG. 7 is a cross-sectional view taken along line 7-7 of FIG. 2according to an embodiment of the invention.

FIG. 8 is an exploded perspective view of a hose connection to the fuelcell stack according to an embodiment of the invention.

FIG. 9 is a schematic diagram of a fuel cell system according to anembodiment of the invention.

DETAILED DESCRIPTION

During the initial startup phase of a fuel cell system, the temperatureof the fuel cell stack typically is significantly lower than its normaloperating temperature. Therefore, for purposes of rapidly warming up thefuel cell stack to the appropriate operating temperature, a fuel cellsystem may bypass the radiator of the coolant subsystem during theinitial startup phase. For purposes of accomplishing this, the fuel cellsystem may include a radiator bypass subsystem, an arrangement includinghoses, hose fittings and a thermostat for purposes of controlling whencoolant flows through the radiator. More specifically, when the fuelcell stack is operating above a predefined threshold temperature, theradiator bypass subsystem routes coolant from the fuel cell stackthrough the radiator. However, when the fuel cell stack has atemperature that is below its desired operating temperature, theradiator bypass subsystem ensures that the coolant bypasses the radiatorto permit rapid warmup of the coolant and fuel cell stack. A challengein using the above-described radiator bypass subsystem is that thesubsystem requires a significant number of components that maysignificantly increase the overall size, complexity and cost of the fuelcell system.

FIG. 1 depicts a system 10 for regulating the flow of coolant through afuel cell stack 14 in accordance with an embodiment of the invention.More specifically, the fuel cell stack 14 includes an inlet coolantmanifold passageway 25 that extends through the fuel cell stack 14 todeliver coolant to the coolant flow channels formed in certain flowplates 15 of the stack 14. The coolant from the passageway 25 migratesthrough the coolant flow channels and enters an outlet coolant manifoldpassageway 24 that also extends through the stack 14.

For purposes of circulating the coolant through the fuel cell stack 14,the system 10 includes a coolant, pump 40 that pressurizes coolant thatexits the pump 40 to flow through a hose 42 into a coolant inlet port 47of the stack 14. From the coolant inlet port 47, the coolant flows intothe inlet coolant passageway 25, through the flow channels of thevarious coolant flow plates and into the outlet coolant manifoldpassageway 24. A pocket 22, located in a top end plate 16 of the fuelcell stack 14, in some embodiments of the invention, is in communicationwith the passageway 24. As described below, the pocket 22 has a firstoutlet port to provide the outlet coolant flow to a radiator 32 and asecond outlet port that is used to return the coolant to the coolantpump 40 while bypassing the radiator 32. A thermostat 20, disposed inthe pocket, selects the appropriate coolant outlet port to receive theoutlet coolant flow, depending on the temperature of the coolant.

More specifically, during a non-startup phase of the system 10, thecoolant flows from the pocket 22, through an opening 23 (the firstcoolant outlet port) and into an outlet hose 30 that communicates thecoolant to the radiator 32. The radiator 32 removes thermal energy fromthe coolant and returns the coolant (via a hose 34) to the coolant pump40.

The fuel cell stack 14 includes features to rapidly warm up the fuelcell stack 14 during the startup (herein called the “startup phase”) ofthe system 10. More specifically, during the initial startup phase whena temperature of the coolant is below some predefined threshold, thethermostat 20 blocks communication between the outlet of the passageway24 and the hose 30 and opens communication between the coolantpassageway 24 and an opening 52 (the second coolant outlet port) that isconnected to a bypass tube 26.

As depicted in FIG. 1, the bypass tube 26 includes an upper inlet end 27that extends into the pocket 22. From the inlet end 27, the bypass tube26 extends down through the coolant manifold passageway 24 and throughthe flow plates 15 to an end plate 18 of the fuel cell stack 14. Afitting (not depicted in FIG. 1) is sealed to the lower end of thebypass tube 26 to communicate coolant from the bypass tube 26 to a hose43 that returns the coolant to the coolant pump 40. Because thethermostat 20 prevents coolant from entering the hose 30 during theinitial startup phase of the system 10 when the fuel cell stack 14 iswarming up, the coolant bypasses the radiator 32.

When the coolant temperature reaches a predefined threshold, thethermostat 20 closes the communication between the passageway 24 and theinlet end 27 of the bypass tube 26 and opens coolant communication tothe hose 30. Thus, in this state of the thermostat 20, coolant flowsthrough the hose 30 and through the radiator 32 before returning to thecoolant pump 40. Therefore, for this flow path, the radiator 32 removesthermal energy from the coolant to regulate the operating temperature ofthe fuel cell stack 14.

The arrangement that is depicted in FIG. 1 has one or more advantagesover a system that may use a thermostat housing or mounting that isseparate from the fuel cell stack 14. Because the thermostat 20 isintegrated into the fuel cell stack 14, other components of the coolantbypass subsystem, such as the bypass tube 26 (for example), may also beintegrated into the stack 14. More specifically, the arrangement that isdepicted in FIG. 1 eliminates the need for an additional thermostathousing, reduces the potential number of hoses, reduces the potentialnumber of hose connections and eliminates the need for a separate ventto vent air from the stack coolant during filling of the coolant.Furthermore, the arrangement that is depicted in FIG. 1 improves theserviceability of the thermostat and reduces packaging volume thatallows for a smaller system to design. Furthermore, due to the compactarrangement, less heat transfer loss may be incurred to additionalcomponents. Other and/or different advantages may be possible in otherembodiments of the invention.

The end plates 16 and 18, as their names imply, form the upper and lowerboundaries, respectively, of the fuel cell stack 14. A primary functionof the end plates 16 and 18 is to hold the fuel cell flow plates 15 incompression for purposes of energizing seals between the flow plates 15.In some embodiments of the invention, the lower end plate 18 may serveas the service end for the fuel cell stack 14, in that various coolant,fuel, oxidant and electrical connections may be present at this end ofthe stack 14. The flow plates 15 include various flow channels(serpentine surface flow channels, for example) to communicate reactantflows to establish serially-connected fuel cells and to communicate thecoolant flow throughout the fuel cell stack 14. The fuel cell stack 14also includes various gaskets, gas diffusion layers, PEMs, etc., forpurposes of forming the fuel cells. Furthermore, the flow plates 15 eachincludes manifold openings, for inlet and outlet coolant flows, fuelflows and oxidant flows. When the flow plates 15 are aligned to form thefuel cell stack 14, these openings align to form the various manifoldpassageways through the stack 14, such as the coolant passageways 24 and25.

FIG. 2 depicts a top view of the end plate 16 of the fuel cell stack 14according to an embodiment of the invention. As shown, the end plate 16includes the pocket 22 that is formed in the end plate 16 for housingthe thermostat 20 (not depicted in FIG. 2). The pocket 22 is alignedover the top end opening of the coolant outlet manifold passageway 24.The pocket 22 includes the lower opening 52 that receives the bypasstube 26. As depicted in FIG. 2, the pocket 22 also includes twoadditional openings 50, each of which partially circumscribes theopening 52. The openings 50 serve as ports to receive coolant flow fromthe coolant manifold passageway 24. The opening 52 is circumscribed by aboss 54, the inner diameter of which closely matches the outer diameterof the bypass tube 26 to hold the bypass tube 26 to the pocket 22.

In some embodiments of the invention, the lower end of the bypass tube26 may form a similar connection with the lower end plate 18 in that aboss (not shown) of the lower end plate 18 receives the lower end of thetube 26. For these embodiments of the invention, the boss in the lowerend plate 18 may contain an internal annular shoulder to limit thedownward travel of the bypass tube 26.

The pocket 22 may be generally tapered, in that the top opening 23 ofthe pocket 22 is larger than the bottom opening 52, in some embodimentsof the invention. The top opening 23 is adapted to receive an outlethose fitting (not depicted in FIG. 2) that communicates coolant out ofthe stack 14 when the stack 14 has reached its operating temperature.The thermostat 20, however, during the initial warmup of coolant, blockscoolant flow to the outlet hose fitting so that coolant flows backthrough the opening 52 and into the bypass tube 26.

The stack includes various regions 70, 74, 75, 77 and 78, each of whichis constructed to seal off a particular manifold passageway. Forexample, the region 75 is constructed to form a seal with the top end ofthe inlet coolant manifold passageway 25. Likewise, the regions 70, 74,77 and 78 are designed to form seals with the top ends of the inlet andoutlet fuel and oxidant manifold passageways. The end plate 16 alsoincludes openings 80 that receive bolts that extend to the lower endplate 18. These bolts connect the end plates 16 and 18 for purposes ofmaintaining a compression of the flow plates 15 that are disposed inbetween. More specifically, in some embodiments of the invention, thesebolts extend along the outside of the flow plates 15.

Referring to FIG. 3, in some embodiments of the invention, the end plate16 is generally planar and may include a raised extension 90 on itsupper surface to form part of the pocket 22. In other embodiments of theinvention, the thermostat may be located entirely inside the planarportion of the end plate 16. Thus, many other embodiments arecontemplated and are within the scope of the appended claims. As alsodepicted in FIG. 3, the boss 54 generally extends below the generalplane of the plate 16 and into the outlet coolant manifold passageway 24to receive the bypass tube 26.

As depicted by the reference numerals 100 in FIG. 4 (depicting a bottomview of the end plate 16), the port openings 50 may be generallytapered. Furthermore, the regions of the plate 16 that surround theopenings 70, 74, 75, 77 and 78 may also be tapered.

As a more specific example, FIG. 5 depicts a more detailed view of thepocket 22 in accordance with some embodiments of the invention, takenalong line 5-5 of FIG. 2. As shown, the pocket 22 includes regions 121,established by the openings 50, that permit coolant flow into the pocket22. Furthermore, the bypass tube is received in the opening 52. Asshown, the pocket 22 may be generally symmetrical about a longitudinalaxis 129. The pocket 22 may also include an annular groove 124 that islocated near the opening 23. The groove 125 circumscribes thelongitudinal axis 129. The groove 124 is formed in the body 120 of thepocket 22 and as described further below, is adapted to receive aflanged end of a hose fitting and also receive a flange of thethermostat 20, in some embodiments of the invention.

More specifically, FIG. 6 depicts a hose fitting 130 and the thermostat20 that are mounted inside the pocket 22 in accordance with someembodiments of the invention. The hose fitting 130 is designed so that alower end 135 of the fitting 130 may be inserted into the opening 130.

As also depicted in FIG. 6, the longitudinal axis of the thermostat 20may be generally concentric with the longitudinal axis 129 of thepocket. The thermostat 20 may be suspended inside the pocket 22 by aradial flange 140 (of the thermostat 20) that circumscribes the mainbody of the thermostat 20 and rests on a lower shoulder 127 of thegroove 124. The end 135 of the fitting 130 is above the flange 140; andthe shoulder 127 is below the flange 140. Thus, the fitting 130 servesto lock the thermostat 20 in place inside the pocket 22. As alsodepicted in FIG. 6, in some embodiments of the invention, a seal 126 (anO-ring, for example) may be located inside the annular groove 124between the end 135 and wall of the pocket 22.

The thermostat 20 operates in the following manner, in some embodimentsof the invention. The thermostat 20 includes a mandrel, a top end 148and a lower end 150 of which are depicted in FIG. 6. The thermostat 20also includes ports (not depicted in FIG. 6) that are opened and closedby movement of this mandrel. In the state of the thermostat 20 depictedin FIG. 6, the mandrel is at its uppermost position to block offcommunication through the thermostat 20. Therefore, in the depictedposition, coolant does not flow through the thermostat 20; and thus,coolant does not flow through an outlet port 131 of the hose fitting130. The lower end 150 of the mandrel includes a sealing flange 151 thatseals off the top end 27 of the bypass tube 126 when the mandrel is inits lowermost position. In the position depicted in FIG. 6, the mandrelis in its uppermost position. Therefore, in this position, the flange151 is removed from the valve seat presented by the top end surface ofthe bypass tube 26 to allow coolant to flow from the coolant passagewayof the stack back into a central passageway 160 of the bypass tube 26.

The state that is depicted in FIG. 6 is for the condition in which thesystem 10 is in the startup phase and the coolant has not reached theappropriate temperature to cause the thermostat 20 to close off flowthrough the bypass tube 26 and permit coolant to flow from the coolantpassageway of the stack out of the hose fitting 130. However, when thecoolant reaches the predefined temperature threshold, the mandrel of thethermostat 20 moves in a downward direction so that the sealing flange151 seals off the bypass tube 26. Furthermore, in this lower position ofthe mandrel, the thermostat 20 allows coolant to pass through thethermostat 20 into the fitting 130, out of an outlet 131 and into thehose 30 (see also FIG. 1).

In some embodiments of the invention, the thermostat 20 may be driven bya wax motor. In this regard, in a relatively unexpanded state of thewax, the mandrel of the thermostat 20 remains in the upper positiondepicted in FIG. 6. However, as the temperature of the coolantincreases, the wax expands to drive the mandrel in a downward directionto seal off the bypass tube 26 in open communication to the outlet 131and thus, to the radiator 32 (see also FIG. 1).

Among the other features of the pocket 22, in some embodiments of theinvention, the body 120 of the pocket 22 includes a lower extension 121that circumscribes the perimeter of the top outlet of the coolantmanifold passageway 24. A gasket (not shown) is located between thebottom end of the extension 121 and the uppermost flow plate of thestack 15 to form a seal between the end plate 16 and the rest of thestack 15. Furthermore, in some embodiments of the invention, the upwardextension 90 of the pocket 22 may include an upper flange surface 149for purposes of receiving a flange to lock the fitting 130 in place, asfurther described below.

FIG. 7 depicts a cross-sectional view of the pocket taken along line 7-7of FIG. 2. As shown, except for the ports 50, the pocket 22 is sealedoff from the coolant manifold passageway 24. Thus, in a cross-section ofthe pocket 22 not taken through the port (i.e., the view depicted inFIG. 7), the body 120 of the pocket 22 extends to the boss 54.

FIG. 8 depicts an exploded perspective view of an outlet hose fittingassembly that is connected to the pocket 22. More specifically, thisassembly includes the hose fitting 130 that is held in place by a flange180. More specifically, the lower surface of the flange 180 rests on theflange surface 149 (see FIG. 6) of the pocket 22 and also extendspartially over an upper radial shoulder 133 of the fitting 130. However,to prevent inadvertent removal of the hose fitting 130 from the pocket22, the flange 180 includes screw holes 181 that receive screws to mountthe flange 180 to the service plate 16.

Referring to FIG. 9, in some embodiments of the invention, theintegrated thermostat may be used in a fuel cell system 200. In thesystem 200, the coolant pump 40 (FIG. 1) and the radiator 32 (FIG. 1)are part of an overall coolant subsystem 201 that circulates coolantthrough the fuel cell stack 14. The fuel cell stack 14 receives reactantand oxidant flows from a fuel processor 206 and an air blower 208,respectively. Alternatively, in other embodiments of the invention, thefuel processor 206 may be replaced by a hydrogen supply (a hydrogentank, for example). Control valves 204 of the fuel cell system 200 mayregulate the communication of the fuel and oxidant flows to the fuelcell stack 14. The fuel cell system 200 may also include a powerconditioning subsystem 216 for purposes of communicating power from thefuel cell stack 14 to an external load 250. For example, the powerconditioning subsystem may include, for example, a DC-to-DC converter230 that converts a DC voltage of the fuel cell stack 14 into anothervoltage level (that appears on a terminal 231) that, in turn, isconverted by an inverter 234 to an AC voltage that appears on outputterminals 230 of the fuel cell system 200.

Additionally, the power conditioning subsystem 216 may include varioussensors and monitoring circuits for purposes of controlling operation ofthe power conditioning system and/or for purposes of controllingoperation of the overall fuel cell system 200. For example, the powerconditioning system 216 may include a current sensor 218 for purposes ofmonitoring the current of the fuel cell stack 14 as well as a cellvoltage monitoring circuit 220 for purposes of monitoring individualcell voltages, groups of cell voltages and/or a stack voltage of thefuel cell stack 14.

The various sensors and other circuits communicate (via communicationlines 245) to a controller 240 of the fuel cell system 200. Thecontroller 240 may include, for example, one or more microcontrollers ormicroprocessors, as examples. The controller 240 may include a memory242 that stores program instructions 144 for purposes of programming thecontroller 240 to control the fuel cell system 200. The controller 240communicates with the fuel cell system via several control lines 247. Asexamples, the controller 240 may control operation of the fuel processor206, may control operation of various motors (fan motors, actuatormotors, valve control motors, etc.), control operation of the DC-DCconverter 230, control operation of the inverter 234, control operationof the coolant subsystem 201, etc., depending on the particularembodiment of the invention.

While the invention has been disclosed with respect to a limited numberof embodiments, those skilled in the art, having the benefit of thisdisclosure, will appreciate numerous modifications and variationstherefrom. It is intended that the appended claims cover all suchmodifications and variations as fall within the true spirit and scope ofthe invention.

1. A fuel cell system comprising: a fuel cell stack; a thermostatmounted to the fuel cell stack to regulate a flow of coolant; and abypass tube located inside an internal coolant passageway of the stack,wherein the thermostat regulates flow of the coolant into the bypasstube.
 2. The fuel cell system of claim 1, wherein the thermostat ismounted inside a pocket formed in the fuel cell stack.
 3. The fuel cellsystem of claim 1, wherein the thermostat is mounted inside a pocketformed in an end plate of the fuel cell stack.
 4. The fuel cell systemof claim 1, further comprising: a radiator, wherein the thermostatcontrols whether the flow of coolant flows through the radiator.
 5. Thefuel cell system of claim 1, wherein the thermostat is adapted to opencommunication between the bypass flow tube and the coolant passageway inresponse to the a temperature of the coolant being below a predefinedtemperature threshold.
 6. The fuel cell system of claim 1, furthercomprising: a radiator, wherein the bypass tube is adapted to bypass theradiator when the temperature of the coolant is below the predefinedthreshold.
 7. The fuel cell system of claim 1, wherein the thermostat islocated inside a pocket formed in the stack and the pocket comprises ashoulder to secure a flange of the thermostat to the stack.
 8. The fuelcell system of claim 7, further comprising: an outlet fitting tocommunicate the coolant from the fuel cell stack, the fitting comprisingan end to Jock the flange to the shoulder.
 9. The fuel cell system ofclaim 1, wherein the thermostat is located inside a pocket of the fuelcell stack, the pocket comprising a boss to hold a coolant bypass tube.10. The fuel cell system of claim 1, wherein the thermostat is locatedinside a pocket of the fuel cell stack, the pocket comprising: at leastone port to receive a coolant flow from the fuel cell stack.
 11. Amethod usable with a fuel cell stack, comprising: mounting a thermostatto the fuel cell stack to regulate a flow of coolant; forming a pocketin the stack; disposing the thermostat in the pocket; forming a boss inthe pocket to hold a coolant bypass tube; and routing the bypass tubethrough an internal coolant manifold passageway of the stack.
 12. Themethod of claim 11, further comprising: forming a pocket in the fuelcell stack and disposing the thermostat inside the pocket.
 13. Themethod of claim 11, further comprising: forming a pocket in an end plateof the stack and disposing the thermostat inside the pocket.
 14. Themethod of claim 11, further comprising: operating the thermostat toselectively bypass a radiator.
 15. The method of claim 14, wherein Theselectively bypassing comprises: bypassing the radiator in response to atemperature of the coolant being below a predefined temperaturethreshold.
 16. The method 0f claim 14, wherein the selectively bypassingcomprises: not bypassing the radiator in response to the temperature ofthe coolant exceeding a predefined threshold.
 17. The method of claim11, further comprising: forming a pocket in the fuel cell stack; andforming a shoulder in the pocket to hold a flange of the thermostat. 18.The method of claim 17, further comprising: using an outlet fitting tolock the flange to the shoulder.
 19. A fuel cell system comprising: astructure to form at least one fuel cell, the structure comprising aninternal passageway to communicate coolant to remove thermal energy fromsaid at least one fuel cell; a thermostat mounted to the structure toregulate a flow of coolant; and a heat exchanger bypass tube locatedinside the internal passageway, wherein the thermostat regulates flow ofthe coolant into the bypass tube.
 20. The fuel cell system of claim 19,wherein the thermostat is mounted at least partially inside a pocketformed in the structure.
 21. The fuel cell system of claim 19, furthercomprising: a heat exchanger, wherein the thermostat controls whetherthe flow of coolant flows through the heat exchanger.
 22. A methodusable with a fuel cell stack, comprising: mounting a thermostat to thefuel cell stack to regulate a flow of coolant; disposing a bypass tubein an internal coolant manifold passageway of the stack; and using thethermostat to regulate communication of coolant with the bypass tube.23. The method of claim 22, further comprising: forming a pocket in thefuel cell stack and disposing the thermostat inside the pocket.
 24. Themethod of claim 22, further comprising: forming a pocket in an end plateof the stack and disposing the thermostat inside the pocket.